1. Field of the Invention
The present invention relates to a data decoding apparatus for use in an image file or a facsimile system. The apparatus of the invention is particularly suitable for high-speed decoding of image signals which are run-length-coded by the modified Huffman encoding method (one-dimensional compression) and stored or transmitted.
2. Description of the Prior Art
In conventional apparatuses of this type, when the data effective code lengths vary as in MH codes, processing speed for decoding cannot be kept constant. When printing is to be performed in accordance with decoded signals, a printer is required which is capable of changing the subscanning speed, which is often the paper feed speed. When decoded signals are supplied to a high-speed electrostatic printer which has a predetermined subscanning speed, the decoded signals are first stored in a one-page memory and are then supplied to the printer. Furthermore, since decoding is performed by software processing using a microprocessor, high-speed processing speed cannot be performed.
As mentioned above, since the code lengths vary, after decoding of a code is completed and the subsequent code is to be decoded, a code shift operation time for fetching this subsequent code in the decoding apparatus also varies, causing waiting time in signal processing.
When a decoding error is caused due to a bit drop of a code or the like, color inversion of a monochromatic image can be caused.
When the apparatus is designed for processing with the code having a maximum length, the number of signal lines or the capacity of the memory element and the like must be increased, resulting in higher cost and other disadvantages.